Heat transfer system



Jan. 21, 1941. c. E. STINER 2,229,262

HEAT TRANSFER SYSTEM Filed Feb. 24, 1939 2 Sheets-Sheet 2 Patented Jan.21, 1941 UNITED STATES PATENT OFFICE HEAT TRANSFER SYSTEM poration ofDelaware Application February 24, 1939, Serial No. 258,165

4 Claims.

My invention relates to heat transfer systems, particularly thoseutilized for the elevation of petroleum and its derivatives todistillation and cracking temperatures.

In accordance with U. S. Patent #2,129,589, granted to F. H. Praeger onSeptember 6, 1938, combustion chambers or muffles are provided for thepartial completion of combustion of fuel and for directing burning gaseslaterally across a fire chamber and above and in avoidance of convectivetransfer with floor tubes disposed therebeneath. As shown in saidpatent, the muffles rest upon refractory brickwork which is supportedfrom the floor of the combustion chamber. It has also been proposed tomount the combustion chambers externally of the fire chamber with thedischarge-ends thereof directly adjacent an inner wall of the firechamber. In the latter case, and partly to take care of the largeheat-release, air in excess of that required for combustion flows overthe Walls of the combustion chambers. Nevertheless, the temperature ofthose walls may become excessively high since the only cooling providedtherefor is by the said flow of air; and it is impracticable to supplythat air in amount adequate substantially to reduce the walltemperature. The maintenance due to deterioration of those walls is higheven though expensive refractories be utilized.

It has also been proposed to construct muffles of metal which aresupported upon refractory brickwork. In those cases it has beendifficult to prevent burning or melting of the metal, particularly wherethe muflie joins or rests upon its support, because at that point heatis not removed at high rate and. the temperature rises accordingly.

These prior constructions, even though reasonably satisfactory, leavesomething to be desired in the more efiicient utilization of thecombustion space within the fire chamber, and in the length of theuseful life of the muflles or combustion chambers.

In accord with my invention, the combustion chambers, tubular in form,are constructed of a self-supporting refractory, such as metal, which toas great a degree as possible is chemically inert at incandescence tothe burning combustion gases; and each tubular chamber is provided withmeans at the firing end for the support of the entire chamber from apoint adjacent a side wall; Accordingly, without increase in size of theheater, a greater heater capacity is obtained by the addition of floortubes below the combustion chambers and in the unobstructed spacepreviously occupied by the supporting brickwork. Floor tubes in thisposition increase the fluidconducting heat-absorption areas, which,because of the high rate of heat transfer thereto, ma terially increasesthe permissible throughput for a given outlet temperature withoutincreasing the fire-box temperature; and the addition of two or threefloor tubes directly beneath the combustion chamber Will servematerially to reduce the fire-box temperature where the same" throughputand outlet temperature is desired. Heat is radiated from the walls ofthe combustion chambers at a rate to prevent burning or melting of thewalls thereof; and from every unit area thereof to heat-absorptionsurface to prevent overheating of any part of the combustion chambers;moreover, the supports for the muflles or combustion chambers areentirely outside the zone of combustion and are not subject to burningor melting temperatures.

For a more complete understanding of my invention, reference should nowbe had to the drawings, in which:

Fig. 1 is a side elevation, partly in section, of a heater embodying myinvention; 25

Fig. 2 is a fragmentary sectional view taken-on the line 2-2 of Fig. 1.

Fig. ;3 is a fractional end View of one ofv the combustion chambers,with the burner structure omitted. 30

Fig. 4 is a side-elevation, partly in section, of a heater embodying myinvention in a modified form; and 2 Fig. 5 diagrammatically illustratesadifferent sequence of flow of fluid through the tubes of.. Fig. 4.

Referring to the drawing, I have shown my invention in one form asapplied to an oil or petroleum heater l0, having a roof II, a front walll2, a rearwall I3, and a floor M, respectively formed of firebrick orequivalent, which define a fire chamber l5. The rear wall l3 inconjunction with a sloping portion Ila of the roof forms a convectionsection comprising a plurality of oil- 20 and 2|, and may rest uponintervening supports,-where the length of the tubes is suflicientlygreat Headers interconnecting the floor tubes for serial or parallelflow of fluid have been omitted for the sake of clarity, the flow beingshown diagrammatically.

Within a plurality of muffles or combustion chambers 22 to 25, fuel, asdelivered from burners 26 to 29, as gas, or oil, or both, is burned. Thecombustion of the fuel is partially completed within the muflles, whichguide and direct the gases discharged therefrom, the guiding anddirectional effects being of a character to maintain the currents ofgases above, over, and across the floor tubes [9. As explained in theaforesaid Praeger patent #2,129,589, the floor tubes l9 are disposedbelow and without the currents of gases and absorb heat substantiallysolely by radiation; thereby providing for higher average heat inputs tothe several banks without excessive rates of heat absorption anywhere inthe fluid-conducting tubes. Some of the roof tubes l8, particularlythose near the convection tubes [6, receive heat by radiation andconvection, while the mode of heat-transfer to the tubes I5 is largelyby convection.

The combustion chambers or mufiles 22 to 25 may be of identicalconstruction. More particularly, the mufile 25 is formed of a refractorymetal, as nearly as possible chemically inert and highly resistant todeterioration at incandescence to combustion gases and at incandescencehaving sufficient strength for the entire support thereof from one endthereof. While each mufile may be constructed of an alloy comprisingiron, nickel, and chromium in various proportions, I prefer to utilize astrong heat-resistant alloy steel including nickel 12%, chromium 30%,and carbon maximum, though other equally or greater heatresistant alloysor materials may be utilized; and preferably those having sufficientstrength at operating temperature to be supported from one end thereof.

As illustrated, the muffle 25, of tublar form, is provided with a flange30 through which extend a plurality of bolts 3|, which bolts passthrough the flanges 32a of a collar 32 and through steel sheathing 33provided for the front wall [2 of the heater. The muffles need not be ofcircular cross-section, though in the preferred form of my inventionthey are all illustrated as circular. Adjacent the open end of eachmuille and within collar 32 a refractory insert 31 may be secured, as byscrews, to form a Venturi throat which assists in the introduction ofthe amount of air required for the combustion of fuel introduced by theburner 26. The arrangement is such that the major burning of the fueloccurs at a point to the right of insert 31 (as viewed in Fig. 1) andbeyond the flange 30, wherefore the supporting elements are removed fromthe zone of combustion having the highest temperature; and allportionsof the muflles forming the combustion zone comprise radiating surfaces.My invention is further characterized by locating the supporting ends ofthe muflles in a zone not subject to high, damaging temperatures, andfor the remaining portions of the muflles there is adequate radiation ofheat to the roof and floor tubes to prevent burning or melting or undueshort life of the metal muffles. Where additional supports are desiredthey may take the form of simple rods extending from the outer end ofeach mufile to the floor or tube therebeneath, or to the front wall. Therate of firing is under the control of the respectiveburner-controlvalves 39 to 42. Preferably a passage formed by a metallic wall 44 isprovided for the air supply to the muflles. In

some instances it is desirable to preheat the air prior to admission tothe muflles.

In accord with my invention, the metallic mufiles operated atincandescence and forming radiant sources of heat serve totransmit heatsolely by radiation directly to the roof tubes [8 and the floor tubes H)which are within radiant view thereof. The aforesaid alloy ischaracterized by the large amount of heat radiated therefrom, materiallymore than from silicon carbide and the like. For example, the metallictube has approximately one-third greater heat conductivity than siliconcarbide and is not nearly as great in thickness.

After long continued operation, of a year or more duration, the metalforming the mufiles, which may be relatively thin, as of the order ofmay wear away to some extent as by erosion caused by hard particlescontained in the fuel, by oxidation, acid attack, or by a combination ofall of these causes. The wall thickness of each muflle may finallybecome so thin as to permit the appearance of openings therein.Nevertheless, the muflles may be operated for some time after it appearsthat replacement will soon be necessary. The directional effect upon thegases, while lessened somewhat, is generally sufiicient for thecontinuance of a particular run and is not at all comparable with thosecases Where refractory material fails and drops into the interior of themuffle forming deflectors which may cause the gases to move directlytowards the heat absorption structure. Replacement of the muflles isexceedingly easy since that may be done by merely removing the nuts fromthe bolts 3! and by inserting new mufiles in the place of those whichhave served their usefulness. While other mufile supporting means may beutilized, which provide for the removal of themufiles from without thefire chamber, as by extending the muflles through the front wall, Fig.4, and mounting the Venturi block or insert therein, and while foradditional muflle supports single rods may extend from the outermost endof each muffle to the floor therebeneath, or upwardly to the front wall,I have illustrated and described the preferred form of my invention.

Referring to Fig. 4, I have shown a modified form of my invention asapplied to a heater 50 provided with a plurality of muflles 5i, spacedlaterally along a front wall 52 of the heater, each mufile beingprovided with a Venturi burnerblock 53 and fuel-delivering nozzle 54.Each of muffies 5| is supported from the front wall 52 as by bolts(shown in Figs. 1 to 3). The major part of each muffle extends outwardlyover a plurality of floor tubes 55, and serves to direct currents ofburning combustion gases over, above, and in avoidance of convectivetransfer to the floor tubes 55 therebeneath. Oil entering at 56 passesthrough floor tubes 55, leaving the heater by way of line 60.

A second stream of oil enters at 6| into a lower convection bank 62,through an upper convection bank 51, and by way of transfer line 63enters a plurality of roof tubes 64, leaving the heater by way of line65. Where two streams of oil are heated within the same furnace, it isfrequently desirable to elevate the separate streams of oil, which maybe in liquid or vapor phase, to different discharge temperatures.

To provide independent control of the discharge temperatures, I providea plurality of metallic mufiles 66 disposed laterally across the comvection section. Each mufile 66 extends through the end Wall 61 andthrough the bridge wall 58. Fuel is supplied to each mufile through aburnernozzle 68, substantial combustion of the fuel occurring within thernufiie, and the still-burning gases being discharged outwardly from thebridge wall 58. The combustion of fuel elevates the mufile walls toincandescence, each muffle giving up substantial quantities of heat bydirect radiation to the convection tubes 51 and 62. Heat is absorbed bythe roof and floor tubes from the gases discharged from the muflles 66,to some extent still-burning. These gases, under the influence of thedraft imparted by the stack (not shown), rise and also convectively heatsome of the roof tubes 64.

By varying the rate at which fuel is burned within muflles 55, thetemperature of the stream entering by way of line BI and leaving by wayof line may be controlled. By increasing the rate of fuel consumption,the discharge temperature may be increased. Though the floor tubes 55also absorb additional heat, due to radiation from the flame frommufiies 66, this additional heating may be compensated for by decreasing.the rate of fuel supplied to muffles 5|; thereby to provide a"corresponding decrease in the heat radiated to, and absorbed by, floortubes 55. By dependently adjusting the rates of firing it will be seenthat any desired discharge temperature may be maintained on the streamentering at 6! and leaving at 65 while the same discharge temperature ismaintained on the stream entering at 56 and leaving at 60. Conversely,the outlet temperature of the stream 55 to 60 may be varied and theoutlet temperature of stream 61 to 65 I maintained constant; or bothoutlet temperatures may be simultaneously varied.

As shown in Fig. 5, the tubes 51 are connected directly to roof tubes 64for the stream entering at 56 and leaving at 55, while the streamentering at 61 may pass directly through the tubes 62, the floor tubes55, and leave by way of line 65. In this form of my invention anincrease in the rate of firing with respect to muffies 66 serves toincrease the amount of radiant heat received by tubes 51, as well as toincrease the amount of heat received or absorbed by roof tube 64, andadditionally to increase the heat absorbed by tubes .51 by convection.As before, an increase in the heat absorbed by tube 62 may becompensated for to some extent by decreasing the rate of fuelconsumption within the muffles 5|, which primarily determine the heatabsorbed by floor tubes 55.

The metallic mufiles 6 6 completely enclose the burning fuel and preventflame impingement upon the convection tubes 51 and 52, which areordinarily made of carbon steel, while the tubes 55 and 64 areordinarily made of the more eX- pensive, higher heat-resistant alloys.If desired, the mufiles 66 may be secured to the end wall 6.! in mannershown in Figs. 1 and 2, and above described.

While I have shown particular embodiments of my invention, it will beunderstood that I do not limit myself thereto since many modificationsmay be made and I, therefore, contemplate, by the appended claims, tocover any such modiflcations as fall within the spirit and scope of myinvention.

What I claim is:

1. A furnace comprising a heating chamber traversed by burning gases,beat absorption structure within said chamber comp-rising a bank offloor tubes, combustion chambers, each comprising a tubular radiatingwall of refractory material, means for supporting each combustionchamber from one end of its tubular wall, each of said combustionchambers extending generally horizontally from the supporting means intosaid heating chamber and over and above several of said floor tubes, anup-standing bridge wall forming with a rear wall a convection section,additional combustion chambers, each comprising a tubular radiating wallof refractory metal extending across said convection section andreceiving fuel from without the heater and for discharging the burninggases outwardly away from said bridge wall, and a bank of convectiontubes disposed above and below said last-named mufil-es.

2. Oil-heating apparatus comprising a heating chamber, an up-standingbridge wall forming with a back wall of said fire chamber a convectionsection, a plurality of combustion chambers disposed laterally acrosssaid convection section, each comprising a tubular radiating wall ofrefractory metal extending from the rear wall through said bridge wall,means for effecting combustion of fuel in each of said combustionchambers, separate banks of convection tubes disposed above and belowsaid combustion chambers, and floor tubes and roof tubes respectivelyconnected to said convection tubes above and below said combustionchambers for the passage therethrough of separate streams of oil.

3. Oil-heating apparatus comprising a heating chamber, an up-standingbridge wall forming with .a back wall of said fire chamber a convectionsection, a plurality of combustion chambers disposed laterally acrosssaid convection section, each comprising a tubular radiating wall ofrefractory metal extending from the rear wall through said bridge wall,means for effecting combustion of fuel in each of said combustionchambers, separate banks of convection tubes disposed above and belowsaid combustion chambers, floor tubes and roof tubes respectivelyconnected to said convection tubes above and below said combustionchambers for the passage therethrough of separate streams of oil, andcombustion chambers extending between said roof and floor tubes forburning additional fuel to increase .the heat input to said tubes.

4. Oil-heating apparatus comprising a heating chamber, burners forproducing combustion of fuel and generation of heat within said chamber,oil-conducting heat-absorbing structure within said chamber, .aconvection section receiving the products of combustion from saidchamber, elongated combustion chambers formed of refractory materialextending across said convection section and discharging into saidchamber, means for burning fuel within said combustion chambers to heatthem to heat-radiating temperature, and oil-conducting heat-absorbingstructure disposed on opposite sides of said combustion chambers andreceiving radiant heat therefrom and heat by convection transfer fromsaid products of combustion.

CECIL E. STLN'ER.

